Roll Fuchsia Mac SDK from PPdB-GHCt... to Xkten1Nxc... (#24841)

https://dart.googlesource.com/external/github.com/flutter/engine/+/0a2ffe431f3bb7b455f77841f65833ec062cd888
diff --git a/commits.json b/commits.json
index 08f5ba9..4163cd4 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
-  "external/github.com/flutter/engine":"805a93c098e01d20bd713166d760c80ddb13f88a",
+  "external/github.com/flutter/engine":"0a2ffe431f3bb7b455f77841f65833ec062cd888",
   "external/github.com/flutter/flutter":"a0ba6464089f906fefbf610732b2c9a7b66a1260",
   "sdk":"53c8eda9672fe1555821bfa51e31f3c57683da1d"
 }
\ No newline at end of file